/*
 * Copyright 2002-2017 the original author or authors.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package org.springframework.instrument.classloading.tomcat;

import java.lang.instrument.ClassFileTransformer;
import java.lang.reflect.InvocationTargetException;
import java.lang.reflect.Method;

import org.springframework.core.OverridingClassLoader;
import org.springframework.instrument.classloading.LoadTimeWeaver;
import org.springframework.lang.Nullable;
import org.springframework.util.Assert;
import org.springframework.util.ClassUtils;

/**
 * {@link org.springframework.instrument.classloading.LoadTimeWeaver} implementation
 * for Tomcat's new {@code org.apache.tomcat.InstrumentableClassLoader}.
 * Also capable of handling Spring's TomcatInstrumentableClassLoader when encountered.
 *
 * @author Juergen Hoeller
 * @since 4.0
 */
public class TomcatLoadTimeWeaver implements LoadTimeWeaver {

    private static final String INSTRUMENTABLE_LOADER_CLASS_NAME = "org.apache.tomcat.InstrumentableClassLoader";


    private final ClassLoader classLoader;

    private final Method addTransformerMethod;

    private final Method copyMethod;


    /**
     * Create a new instance of the {@link TomcatLoadTimeWeaver} class using
     * the default {@link ClassLoader class loader}.
     *
     * @see org.springframework.util.ClassUtils#getDefaultClassLoader()
     */
    public TomcatLoadTimeWeaver() {
        this(ClassUtils.getDefaultClassLoader());
    }

    /**
     * Create a new instance of the {@link TomcatLoadTimeWeaver} class using
     * the supplied {@link ClassLoader}.
     *
     * @param classLoader the {@code ClassLoader} to delegate to for weaving
     */
    public TomcatLoadTimeWeaver(@Nullable ClassLoader classLoader) {
        Assert.notNull(classLoader, "ClassLoader must not be null");
        this.classLoader = classLoader;

        Class<?> instrumentableLoaderClass;
        try {
            instrumentableLoaderClass = classLoader.loadClass(INSTRUMENTABLE_LOADER_CLASS_NAME);
            if (!instrumentableLoaderClass.isInstance(classLoader)) {
                // Could still be a custom variant of a convention-compatible ClassLoader
                instrumentableLoaderClass = classLoader.getClass();
            }
        } catch (ClassNotFoundException ex) {
            // We're on an earlier version of Tomcat, probably with Spring's TomcatInstrumentableClassLoader
            instrumentableLoaderClass = classLoader.getClass();
        }

        try {
            this.addTransformerMethod =
                    instrumentableLoaderClass.getMethod("addTransformer", ClassFileTransformer.class);
            // Check for Tomcat's new copyWithoutTransformers on InstrumentableClassLoader first
            Method copyMethod = ClassUtils.getMethodIfAvailable(instrumentableLoaderClass, "copyWithoutTransformers");
            if (copyMethod == null) {
                // Fallback: expecting TomcatInstrumentableClassLoader's getThrowawayClassLoader
                copyMethod = instrumentableLoaderClass.getMethod("getThrowawayClassLoader");
            }
            this.copyMethod = copyMethod;
        } catch (Throwable ex) {
            throw new IllegalStateException(
                    "Could not initialize TomcatLoadTimeWeaver because Tomcat API classes are not available", ex);
        }
    }


    @Override
    public void addTransformer(ClassFileTransformer transformer) {
        try {
            this.addTransformerMethod.invoke(this.classLoader, transformer);
        } catch (InvocationTargetException ex) {
            throw new IllegalStateException("Tomcat addTransformer method threw exception", ex.getCause());
        } catch (Throwable ex) {
            throw new IllegalStateException("Could not invoke Tomcat addTransformer method", ex);
        }
    }

    @Override
    public ClassLoader getInstrumentableClassLoader() {
        return this.classLoader;
    }

    @Override
    public ClassLoader getThrowawayClassLoader() {
        try {
            return new OverridingClassLoader(this.classLoader, (ClassLoader) this.copyMethod.invoke(this.classLoader));
        } catch (InvocationTargetException ex) {
            throw new IllegalStateException("Tomcat copy method threw exception", ex.getCause());
        } catch (Throwable ex) {
            throw new IllegalStateException("Could not invoke Tomcat copy method", ex);
        }
    }

}
